feat: add diffing of lcov files

README.md

@@ -2,7 +2,7 @@
 
 # Diff Cov
 
-Simple CLI to print diffs highlighted with test coverage status
+Simple CLI to print git and lcov diffs highlighted with test coverage status
 
 ![Example Output](assets/example-output.png)
 
@@ -45,6 +45,8 @@ git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/0.x
 
 ## Usage
 
+### Git diff
+
 Before you run `diff-cov` you must run your test suite with coverage and output
 a `lcov` coverage file. You must also have all your changes committed to ensure
 it's included in the output.
@@ -62,3 +64,25 @@ diff-cov --coverageFile coverage/lcov.info
 
 A report is printed at the bottom and colored with a threshold of `90%`
 anything below this percentage coverage will be colored red.
+
+### LCov diff
+
+You can also print the coverage difference between to lcov.info files. To use
+this run your tests with coverage for a first time. After its finished you can
+copy your lcov.info file somewhere for later for example:
+
+```shell
+cp ./lcov.info /tmp/lcov.info
+```
+
+Then you can work on your test and run the tests once more with coverage to
+generate you a new `lcov.info` file. Then you can print the difference in
+coverage between the two files with:
+
+```shell
+diff-cov --compare /tmp/lcov.info
+```
+
+This can come in handy when you need to find out what a test is testing. You
+can create your base coverage file, comment out a test, run the tests again and
+diff the results.

src/index.ts

@@ -5,6 +5,7 @@ import { hideBin } from "yargs/helpers";
 import exec from "./exec";
 
 import report from "./report";
+import lcovDiff from "./lcov-diff";
 
 // eslint-disable-next-line @typescript-eslint/no-var-requires
 const parseDiff = require("./diff-parser");
@@ -21,11 +22,16 @@ const options: { [key: string]: Options } = {
     description: "The path to the lcov report file",
     type: "string",
   },
+  compare: {
+    description: "The path to the lcov report you wish to compare to the `coverage-file`",
+    type: "string",
+  },
 };
 
 type Argv = Arguments<
   Partial<{
     coverageFile: string;
+    compare?: string;
   }>
 >;
 
@@ -36,6 +42,10 @@ export const validate = async (argv: Argv) => {
         `Please ensure you have run tests with coverage enabled.`
     );
   }
+
+  if (argv.compare && !fs.existsSync(argv.compare)) {
+    return new Error(`Lcov compare file must be a valid file '${argv.compare}' provided.`);
+  }
 };
 
 export const run = async (argv = process.argv) => {
@@ -45,13 +55,19 @@ export const run = async (argv = process.argv) => {
     return error(validationError.message);
   }
 
+  const baseCoverage = await parseLcov.default(parsed.coverageFile);
+
+  if (parsed.compare) {
+    const compareCoverage = await parseLcov.default(parsed.compare);
+    return lcovDiff(baseCoverage, compareCoverage);
+  }
+
   const diffText = await exec(`git diff origin/HEAD...HEAD`);
   if (diffText.code > 0) {
     return error("Error loading the diff\n\n" + diffText.stderr);
   }
 
   const diff = parseDiff.default(diffText.stdout);
-  const coverage = await parseLcov.default(parsed.coverageFile);
 
-  report(diff, coverage);
+  report(diff, baseCoverage);
 };

src/lcov-diff.ts

@@ -0,0 +1,40 @@
+const buildCoverageSet = (report: any) => {
+  const set = new Set<string>();
+  for (const coverage of report) {
+    for (const detail of coverage.lines.details) {
+      if (detail.hit > 0) {
+        set.add(`${coverage.file}:${detail.line}`);
+      }
+    }
+  }
+
+  return set;
+};
+
+function setDiff<T>(a: Set<T>, b: Set<T>) {
+  return new Set([...a].filter((x) => !b.has(x)));
+}
+
+export const lcovDiff = async (baseCoverage: any, compareCoverage: any) => {
+  const baseSet = buildCoverageSet(baseCoverage);
+  const compareSet = buildCoverageSet(compareCoverage);
+
+  const map = new Map<string, number>();
+
+  const added = setDiff(baseSet, compareSet);
+  for (const key of added) {
+    map.set(key, 1);
+  }
+
+  const removed = setDiff(compareSet, baseSet);
+  for (const key of removed) {
+    map.set(key, 0);
+  }
+
+  for (const [key, value] of [...map.entries()].sort()) {
+    const color = value > 0 ? "\x1b[32m" : "\x1b[31m";
+    console.log(color, key, "\x1b[0m");
+  }
+};
+
+export default lcovDiff;